This invention relates to a magnetron sputtering source, a vacuum chamber with such a source, a vacuum coating system with such a chamber, and in addition a process technique for such a system, as well as its utilization.
In essence the present invention is based on the need for depositing on large-surface, in particular rectangular substrates with an area of at least 900 cm2, a film having a homogenous thickness distribution, by means of sputter coating, in particular also reactive sputter coating. Such substrates are in particular used in the manufacture of flat panels, normally on glass substrates thinner than 1 mm, such as for TFT panels or plasma display panels (PDP).
When magnetron sputter coating large surfaces, even larger sputter surfaces and consequently larger targets are normally required unless the sputtering source and the substrate are moved relative to each other. However, this results in problems with respect to:
(a) uniformity of the process conditions on the large-surface target, with particular severity in reactive sputter coating;
(b) erosion profile;
(c) cooling; and
(d) strain on the large targets, in particular through atmospheric pressure and coolant pressure.
In order to solve the mechanical strain problem (d), relatively thick target plates have to be used, which in turn reduces the magnetic penetration, and consequently, the electron trap effect for a given electrical input power. If the power is increased this results in cooling problems (c), in particular because elaborate methods are needed for achieving good contact between the target and the cooling medium, and also because of the obstruction resulting from the installations on the back for accommodating the magnets. It is also known that in magnetron sputtering, be it reactive or non-reactive, the target arrangement normally consisting of a sputtering area defining target plate made of the material to be sputtered and a bonded mounting plate, the target is sputter eroded along so-called xe2x80x9crace tracksxe2x80x9d. On the sputter surface one or several circular erosion furrows are created due to the tunnel-shaped magnet fields applied to the target along specific courses, which produce circular zones with elevated plasma density. These occur due to the high electron density in the area of the tunnel-shaped circular magnetron fields (electron traps). Due to these xe2x80x9crace tracksxe2x80x9d, an inhomogenous film thickness distribution occurs already on relatively small-surface coating substrates arranged in front of the magnetron sputtering source. In addition, the target material is inefficiently utilized because the sputter erosion along the xe2x80x9crace tracksxe2x80x9d removes little material from target areas outside these tracks which results in a wave-shaped or furrow-shaped erosion profile. Because of these xe2x80x9crace tracksxe2x80x9d the actually sputtered surface even for a large target is small relative to the substrate surface. To eliminate the effect of said xe2x80x9crace tracksxe2x80x9d on the coating it would be possible to move the sputtering source and the substrate to be coated relative to each other, as mentioned above, however, this results in a lower deposition rate per unit of time. If locally higher sputtering power is used, cooling problems are incurred in systems using relative motion.
In trying to achieve the desired goal basically four complexes of problems (a), (b), and (c), (d) are encountered whose individual solutions aggravate the situation with respect to the others; the solutions are mutually contradictory.
The objective of the present invention is to create a magnetron sputtering source through which said problems can be remedied, that can be implemented in practically any size, and that is capable of economically achieving a homogenous coating thickness distribution on at least one large-surface substrate that is stationary relative to the source. In addition to maintaining highly uniform process conditions the source shall be suitable for sensitive reactive processes with high deposition or coating rates. In reactive processes, inhomogenous xe2x80x9crace trackxe2x80x9d effects lead to known, severe problems due to the large plasma density gradients.
This is achieved by the magnetron sputtering source according to the present invention in which at least two, preferably more than two, electrically isolated long target arrangements are placed parallel to each other at a distance that is significantly smaller than the width of the target arrangement, where each target arrangement has its own electrical connections, and where in addition an anode arrangement is provided. The targets of the target arrangements have preferably rounded corners, following the xe2x80x9crace trackxe2x80x9d paths.
On such a magnetron sputtering source according to the invention with independently controllable electrical power input to the individual target arrangements, the film thickness distribution deposited on the substrate located above can already be significantly improved. The source according to the invention can be modularly adapted to any substrate size to be coated.
With respect to the overall arrangement, the anode arrangement canxe2x80x94unless it is temporarily formed by the target arrangements themselvesxe2x80x94be located outside the overall arrangement, but preferably comprises anodes that are installed longitudinally between the target arrangements and/or on the face of the target arrangement, but particularly preferred longitudinally.
Also preferred is a stationary magnetron arrangement on the source; the latter is preferably formed by a magnet frame that encircles all the target arrangements, or is preferably implemented with one frame each encircling each target arrangement. Although it may be feasible and reasonable to implement the magnets on the frame(s), or on the stationary magnet arrangement at least partially by means of controllable electric magnets, the magnets of the arrangement or the frame are preferably implemented with permanent magnets.
Through a corresponding design of said stationary magnet arrangement, preferably the permanent-magnet frames with respect to the magnet field they generate on the immediately adjacent target arrangement, the aforementioned film thickness distribution on the substrate and the utilization efficiency of the long targets can be further enhanced through specific shaping of xe2x80x9crace tracksxe2x80x9d.
Magnet arrangements are provided preferably below each of the at least two target arrangements. These may be locally stationary and be fixed over time in order to create the tunnel shaped magnet field on each of the target arrangements. Preferably they are designed in such a way that they cause a time-dependent variation of the magnet field pattern on the target arrangements. With respect to the design and the generation of the magnet field pattern on each of the target arrangements according to the invention, we refer to EP-A-0 603 587 or U.S. Pat. No. 5,399,253 of the same application, whose respective disclosures are hereby incorporated by reference.
According to FIG. 2 of EPO-A-0 603 587 the location of the magnet pattern and consequently the zones of high plasma density can be changed as a whole, but preferably it is not changed, or changed only insignificantly, whereas according to FIGS. 2 and 3 of said application the location of the apexxe2x80x94the point of maximum plasma densityxe2x80x94is changed.
For changing the location of the zones or the apex on the magnet arrangements, selectively controlled electric magnetsxe2x80x94stationary or movablexe2x80x94can be provided below each of the target arrangements, but far preferably this magnet arrangement is implemented with driven movable permanent magnets.
A preferred, moving magnet arrangement is implemented with at least two magnet drums arranged longitudinally below the driven and pivot bearing mounted target arrangements, again preferably with permanent magnets as illustrated, for an individual target, in FIGS. 3 and 4 of EP-A-0 603 587.
The magnet drums are driven with pendulum motion with a pendulum amplitude of preferably xe2x89xa6xcfx84/4. With respect to this technique and its effect we again refer fully to said EP 0 603 587 or U.S. Pat. No. 5,399,253, respectively, which disclosures are also hereby incorporated by reference.
In summary, at least two driven and pivot bearing mounted permanent magnet drums extending along the longitudinal axis of the target arrangement are preferably provided.
In the preferred manner with the electrical target arrangement supply the field of said stationary magnet arrangement, in particular said frames with the field/time-variable magnet arrangement below each target arrangement, preferably the magnet drums a set of influencing variables is available which in combination allow extensive optimization of the deposited film thickness distribution, in particular with respect to its homogeneity. In addition a high degree of target material utilization is achieved. Highly advantageous is that preferablyxe2x80x94with shift of the magnet field apex on the target arrangementxe2x80x94the plasma zones are not shifted in a scanning manner but that within the zones the plasma density is changed through wobbling.
To allow maximum sputter power input the target arrangements are optimally cooled by mounting them on a base where the target arrangement surfaces facing the base are largely covered by cooling media channels which are sealed against the base by means of foils. Large-surface heat removal is achieved because the pressure of the cooling medium presses the entire foil surface firmly against the target arrangements to be cooled.
On the magnetron sputtering source according to the invention a base, preferably made at least partially from an electrically insulating material, preferably plastic, is provided on which in addition to said target arrangements the anodes and, if existing, the stationary magnet arrangement, preferably permanent magnet frames, the magnet arrangement below the target arrangements, preferably the moving permanent magnet arrangements, in particular said drums, as well as the cooling medium channels, are accommodated. The base is designed and installed in such a way that it separates the vacuum atmosphere and the external atmosphere. In this way the target arrangement can be more flexibly designed with respect to pressure-induced mechanical strain.
Another optimization or manipulated variable for said large-surface film thickness distribution is obtained by providing gas outlet openings, distributed on the longitudinal side of the target arrangement, which openings communicate with a gas distribution system. This makes it possible to admit reactive gas and/or working gas with specifically adjusted distribution into the process chamber above the source according to the invention of a vacuum treatment chamber or system according to the invention.
The rectangular target arrangements are preferably spaced apart by max. 15%, preferably max. 10% or even more preferably max. 7% of their width.
In a preferred design the lateral distance between the individual target arrangements d is:
1 mmxe2x89xa6dxe2x89xa6230 mm, where preferably,
7 mmxe2x89xa6dxe2x89xa620 mm.
Width B of the individual target arrangements is preferably:
60 mmxe2x89xa6Bxe2x89xa6350 mm, and more preferably,
80 mmxe2x89xa6Bxe2x89xa6200 mm.
And, their length L is preferably:
400 mmxe2x89xa6Lxe2x89xa62000 mm.
The length of the individual target arrangements relative to their width is at least the same, preferably considerably longer. Although the sputtering surfaces of the individual target arrangements are flat or pre-shaped and preferably arranged along one plane, it is feasible to arrange the lateral sputtering surfaces closer to the substrate to be coated than the ones in the middle, possible also inclined, in order to compensate any edge effects on the film thickness distribution, if necessary.
The electrons of the magnetron plasma circulate along the xe2x80x9crace tracksxe2x80x9d in a direction defined by the magnet field and the electrical field in the target surface area. It has been observed that the routing of the electron path or its influence upon it and consequently the influence on the resulting erosion furrows on the target surfaces can be specifically optimized by creating the magnet field along the longitudinal axes of the target arrangements and by varying the shape or said field not only with respect to time but also location. With a magnet framexe2x80x94preferably one each, and also preferably one permanent magnet frame eachxe2x80x94this is preferably achieved by positioning and/or by the selected strength of the magnets on the frame, and/or by providing magnet arrangements each below the target arrangements, preferably said permanent magnet drums, by correspondingly varying the strength and/or relative position of the magnets on the magnet arrangement. As the electrons move in a circular path in accordance with the magnet field polarity, it has been observed that apparently due to drift forces the electrons, in particular in the narrow side areas of the target arrangements and in accordance with the direction of their movement, the electrons in corner areas that are diagonally opposite are forced outward. For this reason it is proposed that with the provided magnet frame the field strength created by the frame magnets which are specular symmetrical to the target xe2x80x9crectanglexe2x80x9d diagonal be preferably designed with a locally different shape.
In a preferred design version of the source according to the invention the target arrangements are fixed by means of linear bayonet catches, in particular in combination with their cooling via pressure loaded foils of the aforementioned type. In this way the arrangements can be very easily replaced after the pressure in the cooling medium channels has been relieved; the greater part of the target arrangement back side remains accessible for cooling and no target arrangement fixing devices are exposed toward the process chamber.
A preferred source according to the invention features more than two target arrangements, preferably five or more.
By using a magnetron sputtering source according to the invention on a sputter coating chamber on which, with a clearance from the latter, a substrate holder for at least one, preferably planar substrate to be sputter coated is provided, it is possible to achieve an optimally small ratio VQS between the sputtered source surfaces FQ and the substrate surface PS to be sputtered, where:
VQSxe2x89xa63, preferably
VQSxe2x89xa62, where particularly preferred
1.5xe2x89xa6VQSxe2x89xa62.
This significantly increases the utilization efficiency of the source. In a sputter coating chamber according to the invention with said source this is achieved to an even higher degree by choosing the distance D between the virgin surface of the magnetron sputtering source and the substrate in such a way that it is essentially equal to the width of a longitudinal target arrangement, preferably
60 mmxe2x89xa6Dxe2x89xa6250 mm, and preferably,
60 mmxe2x89xa6Dxe2x89xa6160 mm.
On a vacuum coating system according to the invention with a sputter coating chamber according to the invention and consequently the magnetron sputtering source according to the invention, the target arrangements are each connected to an electrical generator or current sources, where said generators can be controlled independently of each other.
The sputter coating system according to the invention with at least three long target arrangements is preferably operated in such a way that the two outer target arrangements are operated with 5 to 35% more sputtering power, preferably with 10 to 20% more sputtering power than the inner target arrangements. The aforementioned xe2x80x9cscanningxe2x80x9d of the target arrangements with respect to the position of the plasma zones and in particular the preferred xe2x80x9cwobblingxe2x80x9d of the apex of the tunnel magnet fields and consequently the plasma density distribution, preferably realized by means of said magnet drums in pendulum operation, is preferably performed with a frequency of 1 to 4 Hz, preferably approximately 2 Hz. The pendulum amplitude of the drum is preferably {circumflex over ( )}xcfx86xe2x89xa6Π/4 ({circumflex over ( )}xcfx86 meaning the peak value for xcfx86). The coating thickness distribution on the substrate is further optimized through an appropriate design of the path/time profiles of said shift in position.
It should be emphasized that for this purpose also the generators connected to the target arrangements can be controlled for outputting mutually dependent, time modulated signals.
In addition the electrical supply of the target arrangements and/or the distributed gas inlets and/or the magnet field distribution are controlled in such a way or modulated in time in such a way that the desired, preferably homogenous, film thickness distribution on the substrate is achieved.
The magnetron sputtering source is preferably operated with a power density p of:
1 W/cm2xe2x89xa6pxe2x89xa630 W/cm2, 
in particular for reactive film deposition, preferably from metallic targets, and in particular ITO films with:
1 W/cm2xe2x89xa6pxe2x89xa630 W/cm2, 
and for sputter coating metal films preferably with:
15 W/cm2xe2x89xa6pxe2x89xa630 W/cm2. 
As has been recognized in conjunction with the development of said magnetron sputtering source according to the invention, it is basically advantageous, in particular with target plate arrangements that are significantly longer than wide, to design the magnet field strength of the magnetron field, viewed in the longitudinal direction of the target arrangements and in particular their lateral areas, with a locally different shape.
However, this insight is generally applicable to long magnetrons.
For this reason it is proposed for a long magnetron source according to the invention which comprises a time-variable, preferably moving magnet system, to assign a magnet frame to the target arrangement, preferably a permanent magnet frame where the field strength of the frame magnets measured in one given chamber direction, is designed locally different along the longitudinal side of the target arrangements. For compensating said drift forces acting on the circulating electrons it is proposed to design this field strength locally different essentially specular symmetrical to the target diagonal.
The present invention under all its aspects is in particular suited to sputter coating substrates, in particular large-surface and preferably plane substrates by means of a reactive process, preferably with an ITO film (Indium Tin Oxide). The invention is also suited to coating substrates, in particular glass substrates, used in the production of flat panel displays, in particular TFT or PDP panels, where basically the possibility is opened to highly efficiently sputter coat also large substrates, for example, also semiconductor substrates, with minimal reject rates either by means of a reactive or non-reactive process, but in particular also reactive.
Especially in sputter coating processes, in particular in ITO coating, low discharge voltages for achieving high film quality, in particular low film resistances, also without tempering steps, are essential. This is achieved by means of the source according to the invention.
It also achieves effective suppression of are discharges.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.